N/A
The present invention generally relates to centrifuges and in particular to a centrifuge enabling automatic discharge of solids from a separated centrate.
Many different types of centrifugal separators are known for separating heterogeneous mixtures according to xe2x80x9ctheir specific gravities componentsxe2x80x9d. A heterogeneous mixture, which may also be referred to as feed material or liquid feed, is injected into a rotating bowl of the separator. The bowl rotates at high speeds and forces particles of the mixture to separate from the liquid centrate. As a result, a dense solids cake compresses tightly against the surface of the bowl and the liquid centrate forms radially inward from the solids cake.
The bowl may rotate at speeds sufficient to produce 20,000 g""s so that the solids may be separated from the centrate. Typically, the liquid feed travels at a relatively slow speed before being introduced through feed holes to the rotating bowl where the liquid feed is instantaneously accelerated to the angular speed of the rotating bowl. However, introducing the liquid feed to the bowl at such high speeds creates shear forces that often destroy a large amount of the solid component of the liquid feed before separation.
While the solids accumulate along the wall of the bowl, the centrate is drained. Once it is determined that a desired amount of the solids has been accumulated, the separator is placed in a discharge mode. In one such discharge mode, a scraper blade extending the length of the rotating bowl is placed in a scraping position against the separator wall and the bowl is rotated at a low scraping speed. Then, the solids are scraped from the sides of the bowl and fall toward a solids collecting outlet. However, such scraping systems do not effectively remove wet or sticky solids which may have the consistency of peanut butter. In such instances, the sticky solids remain stuck on the separator wall and scraper blades or fall from the wall and then reattach to the blades before reaching the collecting outlet. As a result, the solids recovery yield is reduced and the remaining solids undesirably contaminate the separator.
In accordance with the present invention, a centrifugal separator is provided which automatically discharges solids and maximizes the amount of solids recovery yield and the dryness of the separated solids with minimal user intervention. Full hermetic containment of the separation process is achieved by this centrifugal separator so that automatic xe2x80x9cclean in placexe2x80x9d (C.I.P.) and xe2x80x9csterilization in placexe2x80x9d (S.I.P.) operations may be performed. Accordingly, the centrifugal separator of the present invention is able to perform a wide range of liquid/solid and liquid/liquid separations in biotechnology, pharmaceutical, chemical, food and beverage, and other industrial processes.
The centrifugal separator includes a rotatable separator bowl supported by a hollow shaft spindle. The shaft spindle also supports and positions a scraper and feed assembly for axially moving within the separator bowl. The scraper and feed assembly includes a plurality of scraper blades having a small surface area that extend to substantially the interior surface of the separator bowl. A feed liquid is supplied to the separator bowl by liquid feed passages which pass through the shaft spindle to the scraper and feed assembly so that the feed liquid exits proximate the ends of the scraper blades at substantially the interior surface of the separator bowl. This prevents the feed liquid from being instantaneously over-accelerated due to the angular velocity of the separator bowl. As a result, the feed liquid is subjected to shear forces that are greatly reduced and the feed liquid is less likely to be harmed as compared to the prior art.
The separator bowl is preferably a tubular bowl having a relatively small diameter and a long length. By the use of such tubular separator bowls, high speed operations of the centrifugal separator may be performed to generate separation forces as high as 30,000 g""s at the interior surface of the separator bowl. This allows the feed liquid to be safely and effectively separated at lower stress levels within the separator bowl.
As a result of the high speed operation, the centrifugal separator is able to more effectively separate the solids from the residual liquid so that the dryness of the accumulated solids cake is increased. Even though the scraper blades have a relatively small surface area, the solids from the walls of the separator bowl may be more easily and effectively scraped. To scrape and discharge all of the accumulated solids, the scraper and feed assembly is slowly raised then lowered while the separator bowl is slowly rotated. By the combination of the accumulated solids being drier and the scraper blades having a small scraping surface area, the amount of the discharged solids is greatly increased. The centrifugal separator according to the present invention may thereby be operated aseptically and provide C.I.P. or S.I.P. operations.